1. Field of the Invention
The present invention relates to the field of optical switching. More specifically, the present invention relates to the assembly and packaging of optical switches in an optical cross-connect assembly.
2. Background of Design Considerations
Fiber optic networks transmit optical signals to communicate data within the network. The optical communication signals are transmitted across the networks through a system of optical fibers and optical cross-connect systems. The optical fibers demonstrate a significantly higher bandwidth data transmission capacity and lower signal losses compared to copper wires.
The present invention relates to an optical cross-connect system having optical switches based on micromachines. Micromachines are small electromechanical devices that are fabricated on wafers of silicon and other materials utilizing semiconductor manufacturing techniques. Optical switches in micro-electromechanical systems (MEMS) employ micro-mirrors that are etched onto silicon wafers. Such optical switches are commonly used in fiber-optic networks, which route data carrying light signals between an input and an output. The micro-mirrors typically include an actuator (e.g., a drive motor) that is selectively moves a blocking/reflecting member (e.g., a mirror) between different inputs and outputs, thereby performing the optical switching function. In a fiber optic network, the mirrors can be positioned to block, pass, or reflect (redirect) incoming light beams that are conveyed via individual strands of optical fiber at the inputs to output receivers (e.g., receiving optic fibers). Alternatively in some optical switches, the mirrors can be pivoted to direct the input light beams at a desired angle to the receivers.
In the optical network system, a collimator is provided at the end of each optic fiber, with collimator being mounted or supported in alignment with the specific mirror in the optical switch. To increase the switching capacity of light signals in the network from multiple inputs to multiple output receivers, a number of optical switches are configured in a planar matrix or array to handle switching of data. As the number of channels increases, the number of optical switches increases accordingly. The assembly of optical switches and optic fibers to handle multi-output switching is often referred to as an optical cross-connect.
While fiber optic network systems improve data bandwidth and losses compared to conventional copper wired network, fiber optic network systems pose many new challenges in the design and engineering of the systems. One of the design objectives for an optical cross-connect is to be able to optically connect any input to any output of the cross-connect. To achieve this, the mirrors in each optical switch must be enabled to physically tilt within adequate range to redirect input light signals to any of the output receivers. It can be appreciated that as the number of optical switches and inputs and outputs increases, each mirror needs to be provided with a larger range or angle of motion to serve all the outputs, or the form factor or footprint of the cross-connect assembly must be increased (e.g., increasing the distance between transmitting and receiving mirror arrays) to accommodate the angle limitation of the mirrors in an effort to cover the large span of outputs. For practical applications, there is a limit to the form factor of the cross-connect assembly in installations of the optical network. The limited range of motion of the mirror puts a limitation on the switching capacity of the cross-connect (i.e., puts a limit on the number of optical switches and inputs and outputs that can be configured in an optical cross-connect.) The size of the cross-connect cannot be simply scaled by adding more optical switches. Companies are trying to increase the switching capacity by developing MEMS based optical switches having mirrors with an increased range of motion. The successful development of high capacity optical cross-connect has been limited in part by the development costs, and the structural limitation of the MEMS devices limits.
Further, it is a disadvantage if the mirrors in an array of optical switches are not optimized to maximize the switching coverage within the limits of motion for each mirror. Some of the mirrors may not utilize the full range of motion to cover the possible range of output space; some of the mirrors may be substantially utilized to the limit in one direction and relatively less utilized in the other direction. The unutilized range of the mirrors is in essence wasted resource in the optical cross-connect. If the otherwise unutilized range may be effectively utilized, the overall form factor of the cross-connect assembly may be reduced for a given optical switch array design, or the span of the output receivers may be increased for a given form factor, or the optical switches can adopt a design with a smaller range of motion for a given array size, thus potentially reducing development costs.
It is therefore desirable to develop a configuration of the optical cross-connect that improves switching capacity for a given optical switch design and given limit of mirror motion.
It has been also a challenge to configure the assembly and packaging of optical switches in an optical cross-connect to facilitate coupling of the optic fibers/collimators with respect to the optical switches. For example, the coupling of optic fibers/collimators with the mirrors requires tight tolerances. As the switching capacity of an optical cross-connect increases, the task of aligning the large number of optic fibers/collimators with the mirrors in the switches becomes increasingly more difficult.
It is therefore also desirable to develop a reliable configuration of the optical cross-connect assembly for a large array of optical switches to facilitate optical alignment of the optic fibers and collimators.